Wrong indentation of comments in Emacs

Question

In many languages, the line comment starts with a single symbol, for example # in Python and R.

I find that in Emacs, when writing such line comments, I have to repeat the comment symbol twice to make the correct indentation.

See the following example:

(setq x-select-enable-clipboard t)
                                        ;using a single comment symbol indents wrongly
;; repeating the comment symbol indents fine
(setq-default c-basic-offset 4)

With a single ; at the beginning of the line cannot get the correct indentation. How to get the correct setting? Thanks!

EDIT:

I found the solution myself. In ESS's document:

Comments are also handled specially by ESS, using an idea borrowed from the Emacs-Lisp indentation style. By default, comments beginning with ‘###’ are aligned to the beginning of the line. Comments beginning with ‘##’ are aligned to the current level of indentation for the block containing the comment. Finally, comments beginning with ‘#’ are aligned to a column on the right (the 40th column by default, but this value is controlled by the variable comment-column,) or just after the expression on the line containing the comment if it extends beyond the indentation column. You turn off the default behavior by adding the line (setq ess-fancy-comments nil) to your .emacs file.

So I put this in my .emacs:

(setq ess-fancy-comments nil) ; this is for ESS

I think for Python mode, it has a similar variable.

Answer 1

Your example use Emacs Lisp, in this language the standard convention is that a single ; is indented to the right, whereas two ;; is indented like code would be indented at that point. I strongly recommend that you stick to this convention, otherwise your code would stand out as being different. And three ;;; is indented to the left. Four ;;;; is left indented, and used for major sections. (See https://www.gnu.org/software/emacs/manual/html_node/elisp/Comment-Tips.html)

For Ruby, comments always indent as code, as far as I know.